Why insist on having information in the parameter list which can be derived,
reliably, automatically, from the body of the text? It is definitely
possible to reliably, automatically derive the list of preprocessors; we do
it for every document we print.
I just don't believe this. You can get it right for most sensible
documents, but surely you can't guarantee it. How about
.de TS \" start of spoken text
.in +.5i
.ti -.5i
..
.de TE \" end of text
.br
.sp
..
.TS
all.
(in chorus) go away!
.TE
How does it know this isn't a table? Tbl can make a passable table
from this even, but it wasn't what was intended. I'll bet for any
automated tool you produce, I can generate an example that will be
misinterpreted.
However, this is just trivia, most documents are written to reasonable
conventions. If I write a new preprocessor (I wrote one once to do pie
charts...) how do I signal to you that this new preprocessor is to be
used? Your document examination program will not know about this. It
won't even be aware that you are missing something. The list of
preprocessors seems to be steadily growing too. Knowing you are missing
something is probably just as important.
Similarly with Latex/Plain tex. I'm sure if you were creative enough
you could reprogram things to look like another style, or enough of
each to give a program schizophrenia.
If the message states clearly, "this is troff format, you require
preprocessors a,b,c,d,e and macros x,y,z" there is no ambiguity. Your
automated program can be adapted to scan a document and produce a
suitable header line (which can be fixed up before sent if necessary).
Julian.